1. Field of the Invention
This invention relates to a four-cycle heat insulating engine provided with a supercharger consisting of a turbocharger or a compressor.
2. Description of the Prior Art
A conventional heat insulating engine in which ceramic cylinder head liners having cylinder liner portions are fitted in bores in a cylinder head is disclosed in, for example, Japanese Patent Laid-open No. 122765/1984.
In general, in an operation of a gasoline or diesel engine, four strokes, i.e. a suction stroke, a compression stroke, an explosion stroke (combustion stroke) and an exhaust stroke are carried out in order repeatedly. It is only in an explosion stroke among these four strokes that power is generated with torque transmitted to a crankshaft, and, in the other three strokes, the engine is rotated by an inertial force. There are two kinds of systems, i.e. a four cycle engine and a two-cycle engine which employ the operational principles of these strokes. Especially, a four-cycle engine is an engine which requires time corresponding to four strokes of a piston, i.e. two turns of a crankshaft to complete one cycle by carrying out the above-mentioned four operations in every one stroke of the piston. Thus, in a four-cycle engine, one stroke, i.e. sufficiently much time is given for making exhaust and suction strokes, and the volume efficiency and average effective pressure are high. The efficiency of the engine is specially high in a high-speed region, and one explosion stroke is made per two turns of the crankshaft. This enables the thermal load on each part to be reduced.
In such a heat insulating engine, the cylinder head and the combustion chamber in a cylinder formed in the cylinder block are formed in a heat insulating state out of a heat insulating material or a ceramic material, so that the temperature of the interior of the cylinder increases to a high level to cause a decrease in the volume efficiency and engine output. The reasons why these phenomena occur reside in the following. The suction and exhaust valves are provided in the cylinder head so that these valves are close to each other. Moreover, since the cylinder head and cylinder upper portion in the heat insulating engine are formed in a heat insulating manner, the temperatures of the upper portion of the combustion chamber and the inner surface thereof become high, i.e., the temperatures of the exhaust gas and the upper portion of the combustion chamber increase to a considerably high level. Therefore, the suction port and suction air are apt to be influenced by the heat of the exhaust port, upper wall of the combustion chamber and exhaust gas, and the fresh air sucked into the cylinder receives heat from the interior of the cylinder or the inner surface thereof to be heated and expanded. When the suction air is expanded due to such a thermal influence, the suction rate of the air is reduced extremely by, for example, not less than 20% to cause the suction efficiency to decrease.
In an engine of a two-cycle operation, a suction port is provided in a cylinder liner lower portion, and, when an exhaust valve is opened, pressure waves, i.e. pulse waves occur in the cylinder, whereby the exhaust gas is forced out through an exhaust port to carry out the air exchange. The fresh air then flows from the lower portion of the cylinder into a negative pressure zone occurring on the rear side of this exhaust gas. Since the lower portion of the cylinder is not heated to a high temperature as compared with a cylinder head, the fresh air is not influenced much by the temperature of the inner surface of the cylinder lower portion. This indicates that, if the fresh air is sucked from a cylinder lower portion by carrying out a two-cycle operation in, especially, a heat insulating engine, the flow rate of the scavenging air or suction air does not decrease.
A conventional valve mechanism for internal combustion engines, in which suction and exhaust vavles are formed and operated electrically is disclosed in, for example, Japanese Patent Laid-open No. 183805/1983.